Leading UK companies are ignoring British female candidates for boardroom posts and hiring women from overseas. Figures from Cranfield University School of Management, which compiles the Female FTSE 100 report, show that of the 14 women appointed to a directorship of one of the top 100 companies for the first time last year, only one was a British national.

Alison Cooper took up her post as chief executive of Imperial Tobacco last week, making her the second-ever British woman to hold the top role at a FTSE 100 firm, following Katherine Garrett-Cox at Alliance Trust. The three other female Footsie bosses – Angela Ahrends of Burberry, Cynthia Carroll of Anglo American and Marjorie Scardino of Pearson – are all Americans.

Professor Susan Vinnicombe of Cranfield said: "This suggests women have to tick two boxes at once to be appointed to a board. Companies are very conscious of diversity, and an overseas female candidate covers two bases at once. There are more than 2,000 women in the pipeline for FTSE 100 directorships – why do we have to look overseas?"

The 14 new FTSE 100 female directors included three Americans, a New Zealander, a Canadian, a Swede, two Dutchwomen, a Frenchwoman, a Kazakh national, a Singaporean, an Irishwoman and a Zambian. The lone Briton was Julia Wilson at 3i.

One reason for the hirings is that blue-chip UK companies have global operations and boardroom appointments reflect this. But a study by Vinnicombe and two other academics analysing female board hirings over four years in the early Noughties found that 39% were from overseas, compared with only 28% in an equivalent group of men.

Ros Altmann, a former adviser to 10 Downing Street, said: "In the UK there is a taboo for anyone being overtly ambitious, but even more so for women. There has to be some sort of affirmative action if we want to change this situation."